During a recent hive check I found two reasons to clean your bottom boards during the winter months. These are worth doing a couple of times during the winter if not more often. To begin with I do use screened bottom boards on almost all of my hives. From my experience the screened bottoms have seemed to help with air flow and moisture issues. I also have entrance reducers in place beginning in the late fall to lower the risk of yellow jackets and mice getting into the hives.
So what did I find on my recent inspection?
Lots of dead bees! Hundreds of dead bees actually. And they were blocking the hive entrance and keeping air from flowing through the hive. While all of my other hives were able to get out on the occasional nice winter day, the bees in this hive were trapped inside. Of course this is a bad thing when the bees are unable to exit the hive. They need to get out of the hive on these nicer days to relieve themselves. Without this unhealthy conditions can develop within the hive.
Excess moisture in the hive can also be another issue during the winter. Condensation can build up within the hive and drip onto the bees. This makes it hard for the bees to keep warm when outside temperatures drop. I have found screened bottom boards seem to help with the reduction of moisture. Not a complete cure but an improvement. In the case of this particular hive, there were enough dead bees on the bottom board that air was having difficulty flowing in the hive. This lead to high levels of moisture in the hive.
For two very important reasons you should clean off your bottom boards during the winter. First is to make sure, especially if you are using entrance reducers, the bees can get out and back into the hive. The other is to insure adequate air flow can occur within the hive.
How to Clean Your Bottom Boards
The simplest way I have found clean your bottom boards is to use a stick that fits in the entrance of your hives. Simply insert the stick into the opening and sweep the dead bees out of the hive. I prefer to do this on a day when the bees do not want to be out flying. It reduces the chances of killing bees that may be trying to exit for cleansing flights. A few quick sweeps of the bottom board can make sure your bees can come and go from the hive when needed and help to make sure ventilation during winter months is adequate.